If this is a house drop, the line that runs from the provider's pedestal to the house, it is going to be RG-6 cable most likely. A bit larger than one-quarter of an inch in diameter. There is a product for cable television installers that meets your description, coax in conduit, although that's a very loose description in my opinion. Ostensibly it's been created to protect the cable from digging cuts (and you can see how that worked out) and to allow pulling of replacement coax. Typically, the installation puts so many bends into the conduit that friction wins over pulling a new line into the tubing.
You state that you've spliced it, but did you use coaxial connectors including an F-81 barrel to join the connections?
As noted in a previous answer, you may not have enough slack to perform a single connection.
If you've not used "industry standard" connectors and had insufficient weatherproofing/waterproofing, you can be assured of poor signal (ghosting, snow/pixelation) and a quick demise to the splice.
If you've used the correct connectors and good waterproofing, you may get a few months of service from the connection.
Adhesive lined heat shrink tubing provides really good protection, but it has limitations in the underground environment, especially in wet conditions.
In twenty years of cable television service, I've performed (against company policy) underground splices of house drops. Almost always (can't think of an exception) I've had to return to replace the entire drop.
If your cable company charges you to replace a house drop, you can dig your own trench and ask them for a length of coax to replace the entire damaged run. No need to go all "sprinkler-system" on the trench. It's common to use a square edge shovel, stomp it into the ground and wiggle it fore and aft to make a v-shaped trench. Move one blade to the side and repeat until you reach your goal.
Television coaxial cable has no voltage and requires no minimum depth. If you want to ensure future protection, get big-box-store small diameter conduit and trench it in, then put a pull string inside to make the replacement easier.
You'd really want to call the cable company to make the connections at the pedestal and house demarcation box to ensure problem free service.
Cable Television demarcation box
Cable Television pedestal